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| United States Patent |
5,508,121
|
|
Sawa
|
April 16, 1996
|
Nickel hydroxide electrode for use in an alkaline secondary battery
Abstract
A nickel hydroxide electrode useful in an alkaline secondary battery
containing at least one of a copper-based additive or a manganese-based
additive in either a nickel hydrogen active material as applied to a
porous metal substrate, in a porous metal substrate itself, or both. The
copper-based additive is at least member of the group consisting of
copper, cuprous oxide and cupric oxide. The manganese-based additive is at
least member of the group consisting of metal manganese, MnO, Mn.sub.2
O.sub.3, Mn.sub.3 O.sub.4, MnO.sub.2, MnO.sub.3, Mn.sub.2 O.sub.7,
Mn(OH).sub.2, MnCO.sub.3, K.sub.2 MnO.sub.2, and KMnO.sub.4. When the
additive is used in a positive electrode for an alkaline secondary
battery, the rate of absorption of hydrogen gas generated in the battery
is accelerated resulting in a reduction of the internal pressure of the
battery. Further, the excess capacity of the negative electrode in
relation to the capacity of the positive electrode can be reduced
resulting in an increase in the battery capacity per unit volume.
| Inventors:
|
Sawa; Haruo (Iwaki, JP)
|
| Assignee:
|
Furukawa Denchi Kabushiki Kaisha (Kanagawa, JP)
|
| Appl. No.:
|
202072 |
| Filed:
|
February 25, 1994 |
| Current U.S. Class: |
429/59; 429/101; 429/209; 429/223; 429/233; 429/236 |
| Intern'l Class: |
H01M 010/34 |
| Field of Search: |
429/209,220,221,223,224,233,236,59,101
|
References Cited
U.S. Patent Documents
| 4460666 | Jul., 1984 | Dinkler et al. | 429/236.
|
| 5069988 | Dec., 1991 | Tomantschger et al. | 429/221.
|
| 5344728 | Sep., 1994 | Ovshinsky et al. | 429/101.
|
| 5366828 | Nov., 1994 | Struthers | 429/209.
|
Primary Examiner: Bell; Bruce F.
Attorney, Agent or Firm: Breiner & Breiner
Claims
It is claimed:
1. A nickel hydroxide positive electrode comprising a porous metal
substrate, nickel hydroxide active particles, and at least one additive
selected from members of a group consisting of copper-based additives and
manganese-based additives, wherein said copper-based additives are members
of a group consisting of copper, cuprous oxide and cupric oxide; and said
manganese-based additives are members of a group consisting of metal
manganese, MnO, Mn.sub.2 O.sub.3, Mn.sub.3 O.sub.4, MnO.sub.2, MnO.sub.3,
Mn.sub.2 O.sub.7, Mn(OH).sub.2, MnCO.sub.3, K.sub.2 MnO.sub.2, and
KMnO.sub.4 ; and wherein said at least one additive is present in said
electrode such that said at least one additive is present only externally
to outer surface of the nickel hydroxide active particles.
2. A nickel hydroxide positive electrode according to claim 1 wherein said
at least one additive is present in mixture with said nickel hydroxide
active particles.
3. A nickel hydroxide positive electrode according to claim 1 wherein said
at least one additive is present as an integral part of said porous metal
substrate.
4. A nickel hydroxide positive electrode according to claim 1 wherein said
at least one additive is present both in mixture with said nickel
hydroxide active particles and as an integral part of said substrate.
5. A nickel hydroxide positive electrode according to claim 2 or claim 4
wherein said at least one additive in mixture with said nickel hydroxide
active particles is present in an amount of from 0.5 to 10 wt. % based on
the weight of the mixture.
6. A nickel hydroxide positive electrode according to claim 3 or claim 4
wherein said at least one additive incorporated in said substrate is
present in an amount of from about 2 to 10 wt. % based on the total weight
of the substrate.
7. A nickel hydroxide positive electrode according to claims 1, 2 or 4
wherein said nickel hydroxide active particles are additionally mixed with
a binder.
8. A nickel hydroxide positive electrode according to claims 1, 2 or 4
wherein said nickel hydroxide active particles are additionally mixed with
a thickener.
9. A nickel hydroxide positive electrode according to claims 1, 2, 3 or 4
in combination with a negative electrode; an electrolyte solution; and a
container for containing said positive electrode, said negative electrode
and said electrolyte solution in a sealed manner to provide an alkaline
storage battery.
Description
FIELD OF THE INVENTION
The invention relates to nickel hydroxide electrodes suitable for use in
alkaline secondary batteries.
BACKGROUND OF THE INVENTION
Paste and sintered nickel hydroxide electrodes are known for use as
positive electrodes for alkaline secondary batteries, such as a
nickel-cadmium battery, a nickel-hydrogen battery and the like. In both
paste and sintered electrodes, the positive active material utilized is
nickel hydroxide, which serves as the main active component, and nickel or
cobalt, which serve as an auxiliary electro-conductive component. The
positive active material is contained on or in a substrate, for example, a
foam nickel substrate for a paste electrode and a sintered nickel
substrate for a sintered electrode.
Conventional alkaline secondary batteries as described above, however, have
various defects. Conventional nickel hydroxide electrodes have a very slow
absorption rate for hydrogen gas generated from the negative electrode at
the time of charging due to the oxidation of the hydrogen gas to water.
Therefore, in a sealed nickel-cadmium battery or a sealed nickel-hydrogen
battery, the negative electrode is generally required to be provided with
a larger capacity than the positive electrode in order to provide for the
generation of oxygen gas prior to the generation of hydrogen gas and
thereby the absorption of the hydrogen gas at the negative electrode by
reduction. This results in an increase in the volume of the battery.
However, there are limits to providing an excessive capacity to the
negative electrode as compared to the capacity of the positive electrode
since the volume of the battery to be produced is limited. Contrarily, if
the capacity of the negative electrode is decreased, the volume or
capacity of the battery is also decreased which is not desirable. Further,
in a nickel-hydrogen battery, the hydrogen gas is emitted directly from
the hydride of the negative electrode which increases the internal
pressure in the battery. The released hydrogen gas is also flammable and
susceptible to leaking.
OBJECTS AND BRIEF DESCRIPTION OF THE INVENTION
The present invention solves the above-described problems by providing a
nickel hydroxide electrode, which when used as a positive electrode in an
alkaline secondary battery, has an increased absorption rate for hydrogen
gas generated by the negative electrode. Accordingly, as compared to
conventional batteries, the excess capacity of the negative electrode, in
relation to the capacity of the positive electrode, can be reduced.
Further, the internal pressure o the sealed battery is reduced. The nickel
hydroxide electrode of the present invention is characterized by the
inclusion of at least one of a copper-based additive or a manganese-based
additive, either in the positive active material of the electrode, in a
porous metal substrate of the electrode which is utilized with a positive
active material, or in both.
The copper-based additive is at least one component selected from the group
consisting of copper, cuprous oxide and cupric oxide. The manganese-based
additive is at least one component selected from the group consisting of
metal manganese, MnO, Mn.sub.2 O.sub.3, Mn.sub.3 O.sub.4, MnO.sub.2,
MnO.sub.3, Mn.sub.2 O.sub.7, Mn(OH).sub.2, MnCO.sub.3, K.sub.2 MnO.sub.2,
and KMnO.sub.4.
The positive active material for use in the positive electrode is a mixture
comprising a major amount of a nickel hydroxide active powder material and
a minor amount of a binder material such as a synthetic resin powder or
the like. The mixture can also include a thickener, such as an aqueous
solution of carboxymethylcellulose (CMC) or the like, to form a paste.
The porous metal substrate to be used in the positive electrode is
conventional in nature and is generally in the form of a plate or sheet
made of nickel or nickel-plated steel. The substrate can be a punched or
perforated sheet, an expanded plate, or the like.
The copper-based additive and the manganese-based additive, when included
in a nickel hydroxide electrode of an alkaline secondary battery, are
oxidized at the time of charging to a higher oxide which has the ability
to quickly absorb hydrogen gas when it contacts the hydrogen gas. Even
after the oxide has been reduced as a result of the absorption of hydrogen
gas, the reduced additive can be oxidized again by the continued charging
operation. Thus, the additive can be utilized repeatedly. Accordingly, a
nickel hydroxide electrode containing at least one of the copper-based or
manganese-based additives exhibits quick hydrogen gas absorptivity
continuously. Presently, the specific reason why the higher or highest
oxides have the ability to absorb hydrogen gas as above described is not
finally understood. However, it has been determined that when a nickel
hydroxide positive electrode contains the copper-based and/or
manganese-based additive(s), the absorption rate of hydrogen gas by the
positive electrode is unexpectedly and remarkably accelerated. As a
result, a sealed alkaline secondary battery is obtained which has a
decreased rise in internal pressure as caused by the generation of
hydrogen gas, as compared to conventional nickel hydroxide electrodes.
The additive(s) of the invention are contained in the positive active
material of the electrode in an amount of preferably about 0.5-10 wt. %
based on the total weight of the positive active material. If the additive
amount is less than 0.5 wt. %, little effect is observed. If the additive
amount is greater than 11 wt. %, the amount of the nickel hydroxide active
material is not great enough to provide a battery with a high capacity.
In manufacturing conventional porous metal substrates for an electrode,
such as a foam nickel substrate plate, a sintered nickel substrate plate
or the like, a minor amount of the copper-based additive(s) and/or
manganese-based additive(s) can be mixed uniformly as a raw material in
the manufacture of the substrates. Thus, any type of porous metal
substrate plate or sheet containing the additive can be manufactured. The
amount of the additive(s) contained in the porous metal substrate is
generally from about 2-10 wt. % based on the total weight of the substrate
raw materials. If the amount of the additive(s) in the substrate is too
large, the electroconductivity of the substrate is reduced.
Providing a porous metal substrate containing the copper-based additive(s)
and/or manganese-based additive(s) uniformly distributed over the exterior
surfaces of the porous metal substrate is advantageous since the
additive(s) are then brought into contact with the nickel hydroxide active
material particles when they are coated onto and fill in the pores of the
porous metal substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of a gas measuring apparatus as used in carrying
out the tests described below.
FIG. 2 is a graph showing the hydrogen gas absorptive rate curves for one
set of test electrodes as described below with regard to the amount of
hydrogen gas absorbed by the test electrodes in a completely charged state
and under the application of current, and a theoretical amount of gas
generation calculated from the quantity of applied electricity.
FIG. 3 is a graph showing the hydrogen gas absorptive rate curves of a
second set of test electrodes as described below with regard to the amount
of hydrogen gas absorbed by the test electrodes in a completely charged
state and without application of current, and a theoretical amount of gas
generation calculated from the quantity of applied electricity.
FIG. 4 is a graph similar to that described in relation to FIG. 2 with
respect to a third set of test electrodes as described below.
FIG. 5 is a graph similar to that described in relation to FIG. 3 with
respect to a fourth set of test electrodes as described below.
DETAILED DESCRIPTION AND PRESENTLY PREFERRED EMBODIMENTS
Presently preferred embodiments of the invention are described below.
Example 1
A nickel hydroxide powder serving as an active material, copper powder
serving as an additive according to the present invention, and
tetrafluoroethylene powder serving as a binder were mixed together in a
ratio of 87:10:3 by weight. The resultant mixture, which is referred to
herein as "an active material mixture", was applied to a foam nickel
substrate plate so as to fill in the pores of the plate. The plate with
the active material mixture was compressed at a pressure of 3 t/cm.sup.2
(where "t"=metric ton) to obtain a disc-shaped nickel hydroxide electrode
20 mm in diameter which is referred to as "Electrode A".
Example 2
In this example, one-half the amount of the metal copper powder used in
Example 1 was replaced with a nickel powder. In particular, a nickel
hydroxide powder, copper powder, nickel powder and tetrafluoroethylene
powder were mixed together in the ratio of 87:5:5:3. The resultant active
material mixture was applied to a foam nickel substrate plate so as to
fill in the pores of the plate. The plate with the active material mixture
was then compressed at a pressure of 3 t/cm.sup.2 to obtain a disc-shaped
nickel hydroxide electrode 20 mm in diameter which is referred to as
"Electrode B".
Comparison Example 3
For the purpose of comparison, the copper powder used in Example 1 was
totally replaced with a nickel powder. Specifically, a nickel hydroxide
powder, a nickel powder and a tetrafluoroethylene powder were mixed
together in a ratio of 87:10:3. The resultant active material mixture was
applied on a foam nickel substrate plate so as to fill in the pores of the
plate. The plate with the active material mixture was compressed at a
pressure of 3 t/cm.sup.2, to obtain a disc-shaped nickel hydroxide
electrode 20 mm in diameter which is referred to as "Electrode C".
Electrodes A and B according to the present invention and Electrode C
according to the conventional art were tested using a gas measuring
apparatus to obtain their respective abilities to absorb hydrogen gas.
FIG. 1 shows a schematic of the gas measuring apparatus utilized in
conducting the tests. A first container 1 holds 30 wt. % of a potassium
hydroxide electrolyte solution 2. A second container 3 holds the same
potassium hydroxide electrolyte solution 2. A conduit 4 connects first
container 1 and second container 3. A gas buret 5 is used to
quantitatively measure the gas collected or captured. An open end of the
gas buret is submerged in the electrolyte solution 2 in the first
container 1 for collecting gas.
Test 1
Test 1 was initially conducted with Electrode A. Electrode A was attached
to the L-shaped, bent lower end of a lead wire 6 submerged in electrolyte
solution 2 and positioned horizontally below the open end of gas buret 5.
A disc-shaped nickel plate 8 attached to the L-shaped, bent lower end of a
lead wire 7 was positioned below and parallel at a spaced distance of 5 mm
from Electrode A. Further, a rectangular nickel plate 10 attached to the
lower end of a lead wire 9 was submerged in electrolyte solution 2 of the
second container 3.
Using nickel plate 10 as a counter electrode, Electrode A, was charged with
an electric current amounting to 15 milliampere (mA) per 1 gram of the
nickel electrode until Electrode A became completely charged. Thereafter,
the counter electrode was shifted from nickel plate 10 to nickel plate 8
facing Electrode A and electric current applied to Electrode A and nickel
plate 8 for charging. In this operation, all the hydrogen gas generated
from nickel plate 8 comes into contact with Electrode A. Oxygen gas is
generated from Electrode A during this operation. The oxygen gas and the
hydrogen gas not absorbed by Electrode A was collected by gas buret 5 and
the amount or quantity of the gas collected measured. By deducting the
amount of the collected gas from a theoretical amount or quantity of
generated hydrogen gas and oxygen gas calculated on the basis of the
charging current and time (i.e., the quantity of applied electricity), the
amount or quantity of hydrogen gas absorbed by Electrode A was obtained.
Each of Electrode B and Electrode C were in turn tested in the same manner
as Electrode A as described above. The amount of hydrogen gas absorbed by
each of Electrode B and Electrode C was obtained.
The results of the foregoing tests are shown in FIG. 2. FIG. 2 shows curves
representing the relationship between the amount of gas generation
calculated from the quantity of applied electricity and the amount of
hydrogen gas absorbed by each of Electrodes A, B, and C. Symbols a, b and
c indicate the curves of the hydrogen gas absorption rate of Electrode A,
Electrode B and Electrode C, respectively. As clear from FIG. 2, when the
nickel hydroxide electrode contains a copper additive, the rate of
absorption of hydrogen gas is accelerated and improved.
Test 2
Test 2 was carried out on Electrodes A, B and C as prepared above. After
Electrode A was completely charged by applying an electric current
amounting to 15 mA per 1 gram of the nickel electrode used as a counter
electrode in the same manner as described above in Test 1, the electric
current application to Electrode A was stopped. Nickel plate 8 serving as
a negative electrode and nickel plate 10 serving as a positive electrode
were then connected together. Electric current was applied therebetween in
the same manner described in Test 1. Electrode A in a completely charged
state without further application of electric current was then exposed to
hydrogen gas generated from nickel plate 8. The hydrogen gas which was not
absorbed by Electrode A was collected by gas buret 5 and the amount of
collected gas measured. By deducting the measured amount of collected gas
from a theoretical amount of generated hydrogen gas and oxygen calculated
on the basis of the charging current and time (i.e., quantity of applied
electricity), the amount of hydrogen gas absorbed by Electrode A was
obtained. Test 2 was also carried out in the same manner with each of
Electrode B and Electrode C.
The results of Test 2 with respect to Electrodes A, B and C are shown in
FIG. 3. FIG. 3 shows the relationship between the amount of gas generation
calculated from the quantity of applied electricity and the amount of
hydrogen gas actually absorbed by each of Electrodes A, B and C. Symbols
a', b' and c' indicate the curves of hydrogen gas absorption rate of
Electrode A, Electrode B and Electrode C, respectively. As clear from FIG.
3, when the nickel hydroxide electrode contains a copper additive, the
rate of absorption of hydrogen gas is accelerated and improved.
Additional electrodes were made which, rather than including copper powder,
included respectively, cuprous oxide powder alone, cupric oxide powder
alone, and various mixtures of two or three of copper powder, cuprous
oxide powder and cupric oxide powder, together with nickel hydroxide
active powder in the same manner as described above. Tests 1 and 2 for
measuring hydrogen absorption were then carried out on these respective
nickel hydroxide electrodes in the same manner as described above. The
same trends, i.e., hydrogen absorption rate curves as shown in FIGS. 2 and
3, were observed. Accordingly, the same advantageous acceleration of
hydrogen gas absorption was obtained by nickel hydroxide electrodes
containing each copper-based additive alone and mixtures of the
copper-based additives.
Example 4
Sealed AA-size storage batteries were manufactured using as a positive
electrode nickel hydroxide electrodes according to the present invention.
The electrodes were manufactured using, respectively, active material
mixtures prepared by adding with a nickel hydroxide active material each
of a copper powder, a cuprous oxide powder and a cupric oxide powder. The
respective active material mixtures each further included a CMC aqueous
solution as a thickener to form a paste. The paste mixtures were applied
to separate porous metal substrate plates so as to fill in the pores of
the plates. The plates were then pressed to a predetermined thickness.
The internal pressure of the sealed batteries using the nickel hydroxide
electrodes as described above in a completely charged state was reduced
1/2 to 1/5 as compared to the internal pressure of a conventional
nickel-hydroxide battery. In a nickel-cadmium battery, even when the ratio
of the negative electrode's capacity to the positive electrode's capacity
was lowered from 1.7 to 1.4, the internal pressure of the battery was not
increased. As a result, the battery capacity per unit volume was able to
be reduced by about 10%.
Example 5
As an alternative to adding one or more copper-based additives to the
nickel hydroxide active material, one or more of the copper-based
additives can be added to a porous metal substrate, such as a foam nickel
substrate plate, a punched plate or the like. The additive(s) can be added
as a raw material in the manufacture of the porous metal substrate in an
amount of about 2-10 wt. % based on the total weight of the substrate
plate. In this manner, the copper-based additive particles will be
distributed uniformly over the exterior surfaces of the substrate. A
conventional nickel hydroxide active material mixture is used with the
substrate. An active material mixture useful with the substrate can
include a nickel hydroxide active powder material as a main component and,
as minor components, an electroconductive material such as a nickel
powder, a cobalt powder or the like, and a binder such as a
tetrafluoroethylene powder. This conventional mixture was applied to the
above described porous metal substrates to make nickel hydroxide
electrodes which were used as positive electrodes in alkaline storage
batteries. The rate of absorption of hydrogen gas for these batteries was
much improved and the internal pressure of the batteries reduced as
compared with conventional alkaline batteries using conventional nickel
hydroxide electrodes.
Thus, one or more copper-based additive(s) can be contained in either the
nickel hydroxide active material of the electrode, in the porous metal
substrate of the electrode, or both.
As set forth above, one or more manganese-based additives can be utilized
in a nickel hydroxide active material, porous metal substrate or both in
the same manner as the copper-based additive(s) to provide a nickel
hydroxide electrode. Each manganese-based additive can be used alone or in
mixtures with another manganese-based additive and/or the copper-based
additive(s). The electrode has improved hydrogen gas absorptivity which
results in the battery containing the electrode having a reduced internal
pressure rise, and the ability to reduce the excess capacity of the
negative electrode.
The manganese-based additive(s) function essentially the same as the
copper-based additive(s). The manganese-based additive(s) as contained in
the nickel hydroxide electrode is oxidized during charging to become a
higher state oxidized manganese compound which has a high absorptivity
with respect to hydrogen gas. The manganese oxides produced absorb
hydrogen gas immediately when they come into contact with hydrogen gas. As
a result, the manganese-based additive is reduced by hydrogen. The reduced
additive, however, is capable of being oxidized again by subsequent
electric charging. Accordingly, the nickel hydroxide electrode including
at least one manganese-based additive according to the present invention
continuously exhibits rapid hydrogen gas absorptivity. Consequently, when
the electrode is used as a positive electrode in an alkaline battery, the
battery has a high rate of absorption of hydrogen gas and the rise in
internal pressure in the battery is reduced.
The manganese-based additive(s) can be included in a nickel hydroxide
active material, in a porous metal substrate (such as a foam metal
substrate, a sintered metal substrate) or both in the same manner as
described for the copper-based additive(s). The manganese-based
additive(s) are utilized in a positive active material mixture in an
amount of about 0.5 to 10 wt. %. The manganese-based additive(s) are
contained as a raw material in a porous metal substrate in an amount about
2 to 10 wt. % based on the total weight of the substrate.
Specific examples of positive electrodes including manganese-based
additive(s) according to the present invention are set forth below.
Example 6
A nickel hydroxide powder serving as an active material, a metal manganese
powder serving as an additive and tetrafluoroethylene powder serving as a
binder were mixed together in a ratio of 87:10:3 by weight. The resultant
mixture was applied to a foam nickel substrate plate to fill in the pores
of the plate. The plate with the active material mixture was compressed at
a pressure of 3 t/cm.sup.2 to obtain a disc-shaped nickel hydroxide
electrode 20 mm in diameter which is referred to as "Electrode D".
Example 7
In this example, one-half the amount of the metal manganese powder used in
Example 6 was replaced with nickel powder. In particular, a nickel
hydroxide powder, manganese powder, nickel powder and tetrafluoroethylene
powder were mixed together in a ratio of 87:5:5:3 by weight. The resultant
active material mixture was applied to a foam nickel substrate plate to
fill in the pores of the plate. The plate with the active material mixture
was compressed at a pressure of 3 t/cm.sup.2 to obtain a disc-shaped
nickel hydroxide electrode 20 mm in diameter which is referred to as
"Electrode E".
A hydrogen gas absorption test was then carried out using Electrode D and
Electrode E and the gas measuring apparatus as shown in FIG. 1. The test
was conducted in the same manner as in Test 1 described above with the
exception that Electrode A was each replaced by Electrode D and Electrode
E.
The results of the tests are shown in FIG. 4. FIG. 4 illustrates the
relationship between the amount of gas generation calculated from the
quantity of applied electricity and the amount of hydrogen gas absorbed by
each of Electrodes D and E. For the purpose of comparison, the test
results obtained with Electrode C (which was prepared using a conventional
composition) is also shown in FIG. 4. The symbols d, e and c indicate the
curves of the hydrogen gas absorption rate of Electrode D, Electrode E and
Electrode C, respectively.
As clear from FIG. 4, when the nickel hydroxide electrode includes a
manganese additive, the rate of absorption of hydrogen gas is accelerated
and improved.
Further, hydrogen gas absorption tests were carried out with respect to
Electrode D and Electrode E using the gas measuring apparatus as shown in
FIG. 1 in the same manner as described in Test 2.
The results of these tests are shown in FIG. 5. FIG. 5 shows the
relationship between the amount of gas generation calculated from the
quantity of applied electricity and the amount of hydrogen gas absorbed
through the hydrogen absorption rate of Electrode D and Electrode E. For
the purpose of comparison, the test results obtained with Electrode C
(which was prepared using a conventional composition) are also shown in
FIG. 5. Symbols d', e', and c' indicate the curves of the hydrogen gas
absorption rate of Electrode D, Electrode E and Electrode C, respectively.
As clear from FIG. 5, when the nickel hydrogen electrode includes a
manganese-based additive, the rate of absorption of hydrogen gas is
accelerated and improved.
Further, in addition to using the metal manganese powder, one or more of
manganese compounds containing oxygen, such as MnO, Mn.sub.2 O.sub.3,
Mn.sub.3 O.sub.4, MnO.sub.2, MnO.sub.3, Mn.sub.2 O.sub.7, Mn(OH).sub.2,
MnCO.sub.3, K.sub.2 MnO.sub.2, and KMnO.sub.4, can be utilized.
Combinations of manganese compounds as above described were added to the
nickel hydrogen active material and nickel hydroxide electrodes prepared
in the same manner as described above. Tests as described above in
relation to Test 1 and Test 2 were carried out using these respective
nickel hydroxide electrodes and the gas measuring apparatus shown in FIG.
1. Essentially the same hydrogen gas absorption rate curves as shown in
FIG. 4 and FIG. 5 were obtained for the electrodes prepared containing a
combination of manganese compounds.
Example 8
Sealed AA-size storage batteries including nickel hydroxide positive
electrodes were manufactured using active material mixtures prepared
utilizing a nickel hydroxide active material, each manganese-based
additive described above individually and a CMC aqueous solution as a
thickener to form a paste. These paste mixtures were then each applied to
separate porous metal substrate plates so as to fill in the pores of the
plates. The plates were pressed to a predetermined thickness. The sealed
nickel-hydroxide batteries produced had an internal pressure which was
reduced 1/2 to 1/5 as compared with the internal pressure of a
conventional nickel-hydroxide battery. When an electrode according to the
invention was used in a nickel-cadmium battery (even when the ratio of the
negative electrode's capacity to the positive electrode's capacity was
reduced from 1.7 to 1.4) the internal pressure of the battery was not
increased. As a result, the battery capacity per unit volume was able to
be reduced by about 10%.
Example 9
Rather than combining a nickel hydroxide active material and at least one
of the manganese-based additives, at least one of the manganese-based
additives can be added to a porous metal substrate plate such as a foam
nickel substrate plate, a nickel sintered substrate plate or the like, as
a raw material in the manufacturing of the porous metal substrate plate.
The manganese-based additive(s) are included in an amount of about 2-10
wt. % based on the total weight of the substrate. Manganese-based additive
particles are thereby distributed uniformly in the exterior surfaces of
the substrate. A conventional nickel hydroxide active material is then
used with the substrate. For example, a nickel hydroxide active material
as a main component is mixed together with, as minor components, an
electro-conductive material such as a nickel powder, a cobalt powder or
the like, and a binder such as a tetrafluoroethylene powder or the like.
This mixture was applied to the above prepared porous metal substrates to
provide nickel hydroxide electrodes according to the present invention.
The nickel hydroxide electrodes were used as positive electrodes in
alkaline storage batteries. When these batteries were used, the rate of
absorption of hydrogen gas was improved and the internal pressure of the
batteries reduced as compared to batteries having conventional nickel
hydroxide electrodes.
Thus, the manganese-based additive(s) can be contained in either the nickel
hydroxide active material, the porous metal substrate, or both and provide
effective results. A primary advantageous effect provided is that the
excessive volume or capacity of the negative electrode in relation to the
capacity of the positive electrode can be reduced due to the accelerated
absorption of hydrogen gas by the positive electrode made according to the
present invention. This results in a decrease in the capacity of the
alkaline battery per unit volume.
As will be apparent to one skilled in the art, various modifications can be
made within the scope of the aforesaid description. Such modifications
being within the ability of one skilled in the art form a part of the
present invention and are embraced by the appended claims.
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